The present invention relates to a thermal dye sublimation-type or wax-type printer system which transfers a printing paper using, a stepping motor and more particularly, to an overhead projector transparency (OHPP) (hereinafter, referred to as a "transparency") having a printing surface discriminating area formed thereon, a method for discriminating the printing, surface of the transparency in a thermal printer and an apparatus appropriate therefor, whereby, only when the transparency is loaded in a cassette tray and the printing surface is determined to be in a proper direction printing is performed.
A general thermal dye sublimation-type color printer stores image data transmitted from a device, such as a computer in a memory transmits the image data stored in the memory to a thermal print head (TPH), and records the transmitted image data on paper. That is, the sublimation-type thermal printer employing the thermal print head (TPH) sublimates ink on an ink ribbon by converting electric energy into thermal energy and represents the image data on the recording paper by adsorbing the sublimated ink thereon.
FIG. 1 is a block diagram showing the configuration of a conventional thermal printer. The conventional thermal printer includes a feeding motor 1 for supplying printing paper loaded in a printing paper cassette tray 6 to a capstan roller 7 and a pinch roller 8, a stepping motor 2 for transferring the printing paper supplied to the capstan roller 7 and the pinch roller 8 in stepwise form, a TPH heat generator 3 for representing image data on the printing paper by converting electric energy into thermal energy a discharging motor 4 for discharging the printing paper, and a CPU 5 for controlling a series of printing operations.
The operation of the thermal printer structured as shown in FIG. 1 will be described briefly as follows. When printing paper is loaded in the printing paper cassette tray 6 and a print command is input, a printing operation begins via a platen while the printing paper is supplied to a position where the capstan roller 7 is engaged with the pinch roller 8. At this time the CPU 5 determines what type of printing, medium (a general printing paper or a transparency) is being printed on using a sensor (not shown), and then sets a heat generating time per line according to respective input information and controls the operation of each block shown in FIG. 1 during the printing, operation.
In the conventional thermal printer, when the printing medium is supplied from the printing paper cassette tray 6, only the type of printing medium (a general printing paper or a transparency) is discriminated thereby performing a printing operation. Also, in the conventional thermal printer, the transparency undergoes a special chemical treatment so that dyes of an ink ribbon can be stably deposited on the printing surface of the transparency according to the heat generation of the thermal print head. Thus, when the heat generation thereof occurs on the transparency surface opposite the printing surface (hereinafter, referred to as an "opposite transparency surface"), the chemical characteristic of the dyes is not consistent with that of the opposite transparency surface, so the dyes of the ink ribbon are not properly deposited on the opposite transparency surface.
Thus, if the transparency is loaded in the printing paper cassette tray 6 so that the opposite transparency surface contacts the thermal print head, a proper image output cannot be obtained even though printing is normally completed, and the surfaces of the ink ribbon and the transparency may be severely damaged due to the heat generation of the thermal print head. Furthermore, the surface of the thermal print head is severely damaged, which causes deterioration of image quality.